The Main Causes of Diarrhoea in Cats

THURS 20 AUG 2020

This article is written by Pet Circle veterinarian, Dr Kes Holliday, DVM

Most cats will have diarrhoea at some point in their lives and there are many possible causes for this. Cats with chronic (long-term) diarrhoea may benefit from eating a sensitive stomach diet such as Royal Canin Digestive Care if other causes for the diarrhoea have been ruled out.

In most cases, acute diarrhoea resolves without treatment within a few days. However it is recommended to see your vet if diarrhoea persists as this can cause weight loss, dehydration and/or electrolyte imbalances.

When to seek veterinary attention:

The main causes of diarrhoea

1. Dietary changes

A sudden change in diet (such as introduction of a new food) can cause mild diarrhoea. This should settle down as your cat's intestines adapt to the new type of food. When introducing your cat to a new diet it is best to do so slowly to try and minimise any such problems.

An upset tummy due to a sudden diet change can also be seen with cats that go outdoors and hunt or scavenge, as spoiled food can cause diarrhoea.

2. Infectious causes

Infections may be caused by viruses, bacteria, or other nasty pathogens. Viral causes of diarrhoea in cats include Feline Panleucopenia Virus, Calicivirus, Feline Leukamia Virus or Feline Infectious Peritonitis. Some of these diseases are preventable, so ensure your cat is up to date with their required vaccinations. Bacteria (such as Salmonella) are another potential cause of infectious diarrhoea in cats.

If the cause is infectious, you're more likely to see the diarrhoea in other cats within your household - particularly in younger cats and kittens.

3. Parasites

Source: Centers for Disease Control and Prevention

Intestinal parasites like hookworms, whipworms, roundworms, Tritrichomonas and Giardia will all cause diarrhoea. Cats can pick up these parasites from eating contaminated meat, drinking contaminated water, as well as coming into contact with infected animals or their faeces.

Ensure your cat is treated for parasites regularly, especially if they go outdoors. Many products offer protection from both fleas and most worms, such as Revolution Plus and Advocate.

Top Cat Parasite Preventatives


Revolution is a handy spot-on which covers fleas, intestinal worms, and heartworm (not to be confused with comprehensive Revolution Plus, which provides extra tick prevention.


Some indoor cats in temperate regions may not require flea or tick prevention, but heartworm and intestinal worming is still required. Milbemax is a great option for complete worming, and is a lovely small tablet!


A great option for indoor cats, Advocate is a monthly spot-on that protects your cat from fleas, heartworm, ear mites, and intestinal worms (apart from tapeworm).

Bravecto Plus

Not to be confused with its sister product Bravecto, Bravecto Plus is a topical given every 2 months which protects your cat from ticks, fleas, heartworm, intestinal worms and ear mites.

Shop All Cat Parasite Prevention

4. Food allergy or intolerance

Food allergies can occur when cats develop an allergy to something present in their diet. This is most commonly a protein such as chicken, beef, dairy, fish, lamb, gluten and egg. You may see other symptoms such as itchy skin or vomiting.

If you suspect that your cat may have a food allergy, consult your veterinarian. They may recommend a dietary trial using an elimination diet which is specifically formulated to be hypoallergenic. If the diarrhoea resolves during the feeding trial, it may indicate a food intolerance which usually requires a special dietary formulation to be fed long term.

Your veterinarian may recommend either a novel protein diet or a hydrolysed protein diet to be fed for at least 2 weeks exclusively.

Examples of hydrolysed protein diets: Royal Canin Veterinary Anallergenic, Royal Canin Veterinary Hypoallergenic, Hills z/d Presciption Skin and Food Sensitivities.

Top Hydrolysed Diets for cats

Royal Canin Anallergenic

Made with hydrolysed feather protein meal, this veterinary diet is scientifically designed with proteins too small to create an allergic response.

Royal Canin Hypoallergenic

Royal Canin Hypoallergenic is made from hydrolysed soy protein to reduce the risk of an adverse food reaction or allergy.

Hills Prescription Diet z/d

Z/d is made from a protein that has been hydrolysed, which means that it does not react with your pets allergy receptors.

Shop All Cat Hypoallergenic Diets

Top Novel Protein Diets for cats

Hills Prescription Diet d/d

Based on venison rather than more common meats like chicken, this diet is also grain, gluten and soy protein free.

Black Hawk Duck and Fish

This diet is formulated with sustainably farmed duck and fish. It is also grain free, instead using tapioca and potato as alternative carbohydrates.

Ziwi Peak Venison

The Venison cat cuisine contains 93% premium New Zealand venison meat, organs, bone, and green mussels. It is also completely grain free .

Feline Natural Chicken and Venison

This all natural, grain free canned cat food is packed with cage free chicken, venison and sustainably sourced New Zealand green lipped mussel.

Shop All Cat Hypoallergenic Diets

5. Inflammatory bowel disease

Inflammatory Bowel Disease (IBD) is a common cause of chronic diarrhoea in cats resulting from inflammation in the intestinal wall. This condition can only be diagnosed definitely by taking a biopsy from the intestinal wall and submitting to a laboratory. In some cases, your veterinarian may diagnose IBD on a basis of exclusion and response to diet.

If your cat has been diagnosed with IBD, a diet specifically formulated for sensitive stomachs can help with management. These include: Royal Canin Digestive Care, Hills Science Sensitive Stomach and Skin and Hills Prescription Gastrointestinal Biome. These diets are designed to be highly digestible and have additional prebiotics (fibre) to support the intestinal microbiome.

6. Intestinal tumours

Source: Long Beach Animal Hospital

Intestinal tumours are more common in older cats and common forms include lymphoma and adenocarcinoma. Tumours can either interfere with absorption of food, or partially obstruct the intestine, both of which will result in diarrhoea. These cancers are diagnosed by your veterinarian via ultrasound, xrays, and an intestinal biopsy.

7. Extra-gastrointestinal (systemic) disease

Systemic diseases such as hyperthyroidism, liver and kidney disease can all cause diarrhoea as a symptom. In any case of persistent diarrhoea, ensure you consult your veterinarian and seek emergency treatment if your cat appears unwell.

A word about probiotics and supplements

While research is generally limited into the proven positive effect of probiotics and gastrointestinal supplements for cats, many cat owners report anecdotally that their kitty's loose stool improves with the introduction of a probiotic.

Top Probiotics for Cats